There are many types of trailers normally pulled by tow vehicles such as automobiles, pick-up trucks, vans, utility trucks, and motor homes. These trailer types include camper trailers, large travel trailers, livestock trailers, boat trailers, enclosed vehicle trailers, flat trailers on which may be used to transport farm machinery, NASCAR-type racing cars, motorcycles and other such equipment, etc. As trailers have become larger, heavier, and varied in design over the years, the support wheels have been moved ever further rearward. While this trend does make the trailer pull straighter and more stable with less sway, however, the negative aspect of this trend is this movement shifts more of the weight of the trailer and its contents to the hitch, thus increasing the tongue weight load applied to the rear of the towing vehicle.
Although it may be conceded that a certain amount of tongue weight on the hitch may be beneficial for traction in slippery conditions to keep the drive wheels from spinning, it should also be pointed out that increasing the tilting moment around the rear axle of the towing vehicle has the effect of decreasing the traction at the steering wheels as well as causing the headlights too shine in beams far to high to be safe. Also, while many tow vehicles have the power to pull a large load, few have the frame strength to safely support a large trailer tongue load applied to the rearmost section of the tow vehicle frame.
It thus becomes necessary to reduce the trailer tongue weight in some circumstances. A number of attempts have been made to make a load carrying dolly which attaches between the tow vehicle and the trailer. An example of such a trailer dolly is found in U.S. Pat. No. 3,345,081 to Hartwig, which is directed to a dolly with a pair of support wheels and horizontal and vertical shock absorbing springs. The wheels are not free castering. U.S. Pat. No. 4,253,679 to Sargent is directed to a trailer dolly with a pair of support wheels and with the trailer hitch mounted forward of the axis of rotation of the support wheels. Each wheel is attached via an independent torsion spring which is adjustable for different trailer weights. Again, the wheels are not free castering. U.S. Pat. No. 4,491,338 to Sheldrake and U.S. Pat. No. 3,888,515 to Winter are dollies which are securely attached to the tow vehicle frame. These require custom installation on each towing vehicle, and attachment and removal is generally complicated. U.S. Pat. No. 5,664,796 to Huyzers is a "vehicle extender" which uses a "single, castor action, load bearing wheel set" which is attached to the extender via a vertical or angled shaft. U.S. Pat. No. 5,382,041 to Keith uses an arm limited dolly that may also scuff tires on the roadway each time the vehicle is turned beyond arm limits. U.S. Pat. No. 5,338,050 to Haire uses a dolly that locks the dolly wheels in a straight forward position during the backing up procedure forcing the tires to scrub the ground if any turning is required causing excessive tire wear. Finally there is a specialty steering dolly-type exemplified by the U.S. Pat. No. 5,531,468 to White, in which the inventor goes to great lengths to provide a steering dolly for insertion between the towing vehicle and the towed vehicle. Again the load carrying wheels do not freely caster, and the device may also be difficult to handle during backing as may be required for parking or the like. The solutions devised by these patents are generally satisfactory in shifting some of the tongue weight away from the tow vehicle and onto the support dolly. However, backing up trailers equipped with these dollies is very difficult since it essentially amounts to the simultaneous backing of two tandem linked trailers. Even in the case of free castering support wheels, the wheels often tend to "scrub" sideways instead of swiveling freely during backing operations.
It is clear, then, that a need exists for an improved trailer support which accepts some of the tongue weight of a trailer, thus shifting it off of the two vehicle. Such a support should have support wheels which freely caster in either forward or reverse directions.